1. Field of the Invention
Multiple port burners for burning a mixture of hydrocarbon gas and air.
2. Description of the Prior Art
Most prior art gas-air mixture burners are of the type in which the flame produced is typical of the Bunsen Burner flame. Such a flame is produced by a substantial laminar jet of mixture issuing from a tube or port. As is well known, for each mixture of gas and air a flame is propagated in such mixture by a combustion wavefront progressing into the mixture at a velocity, usually designated as S.sub.u which, in the case of a laminar jet of a stoichiometric hydrocarbon gas-air mixture, is about 40 cm/sec. If the velocity conditions in the jet are such that there is a region close to the rim of the port at which the component of velocity of the jet in a direction away from the port is equal to S.sub.u for the instance involved, the base of the flame will stabilize at such location. If, however, the velocity of the jet issuing from the port is increased, a point is reached at which the gas velocity exceeds the burning velocity S.sub.u at every point and the combustion wave blows off, extinguishing the flame. Each individual port has a definite blow-off velocity for each gas-air mixture supplied to it. The term "blow-off velocity" as used in the specification and claims herein means that velocity at which, for the gas-air mixture involved and with an isolated port of a given size and with no auxiliary flame sustaining mechanism, the base of a flame at said port will move away from said port and extinguish such flame.
The above phenomenon has imposed a limit on the amount of heat energy which can be delivered by any Bunsen burner type of burner port. Typically such ports have been operated with maximum jet velocities of about two to four times the value of S.sub.u for the mixture supplied to the port. Where it is desired to supply more heat energy than is available from a single burner port, the prior art has produced burners with a multiplicity of such ports. However, the ports were arranged so as to retain essentially the characteristics of isolated ports of the nature already described. As a result, high energy level burners have been quite large. Also, they have had a tendency to be noisy and to generate appreciable quantities of CO in their combustion products.
Chapter 12 of Section 12 of the standard gas engineers handbook of the American Gas Association entitled GAS ENGINEERS HANDBOOK, published in 1966 by The Industrial Press, 93 Worth Street, New York, New York, Library of Congress Catalog Card Number 65-17328, discloses that for stability multiport burners require either operation with primary air less than 100% of the air required for complete combustion, hence producing a secondary air requirement, or auxiliary flame reignition, for example by radiant energy or another jet at right angles to the main jet.
Recent developments of compact high efficiency heat transfer modules, such as those described in the copending application of William H. Hapgood, Ser. No. 737,135, Filed June 14, 1968 and now abandoned, have created the need for a similarly compact, highly efficient burner capable of handling fuel inputs of the order of up to 20,000 BTU per hour per square inch of burner surface or even higher. Prior art type burners have not been able to supply this need.